Why is Nearsightedness in Kids Increasing | Children's Health Blog

Written by: Hiyaguha Cohen

February 04, 2016

health-blog

Myopia Epidemic

Rates of myopia have increased steadily worldwide—in fact, they’ve skyrocketed—and particularly among children in Asian nations.

Back in 1949, the UPA animation studio created the character Mr. Magoo, a nearsighted old codger who got into all sorts of trouble because he couldn’t see where he was going. At the time, and as hard as it may be to believe now, nearsightedness was once a relative rarity, afflicting around 14% of adults aged 25 and older in the US.1 Committee on Vision, National Research Council. 1989.Myopia: Prevalence and Progression. 21 January 2016. https://books.google.com/books?id=rIqyPuupuWQC&pg=PT23&lpg=PT23&dq=myopia+rates+1940&source=bl&ots=3kchRGn5-D&sig=_LlTBV0QWAZE_gLUBjm4W2mg7EY&hl=en&sa=X&ved=0ahUKEwiDzu7f4LvKAhVDy2MKHZl-BnQQ6AEIHTAA#v=onepage&q=myopia%20rates%201940&f=false In Asian countries, the rates hovered around 20 percent for adults and 10 to 20 percent for children.2 Dolgin, Elie. “The Myopia Boom.” 18 March 2015. Nature. 21 January 2016. http://www.nature.com/news/the-myopia-boom-1.17120 But rates of myopia have increased steadily worldwide—in fact, they’ve skyrocketed—and particularly among children in Asian nations. These days, an updated Magoo character might more accurately be a 17-year-old child from Seoul.

In South Korea, a mind-blowing 96 percent of all kids now suffer from myopia, according to a huge survey of 24,000 teenage boys. In Beijing, China, a study of almost 5000 adolescent boys and girls found an 80 percent prevalence. The rates are similar for children throughout Asia, and always higher for teens than for younger children.

Myopia occurs when the eyeball is elongated or the cornea or lens is too curved to refract light properly. According to the American Academy of Opthalmology, “Myopia is a refractive error, which means that the eye does not bend light properly to a single focus to see images clearly, which causes light to refract images so that they don’t come to a single focus.”3 Boyd, Kiersten. “Nearsightedness: What is Myopia?” 1 September 2013. America Academy of Opthalmology. 21 January 2016. http://www.aao.org/eye-health/diseases/myopia-nearsightedness The result is that far away images seem blurry, although objects in close range might be perfectly clear.

Back in the Western world, rates also are climbing. While only 7.2 percent of kids in the UK had myopia in the 1950’s, now, that rate is 16.4 percent, more than double what it was.4 Harley, Nicola. “Children twice as likely to be nearsighted as 50 years ago.” 21 January 2016. The Telegraph. 21 January 2016. http://www.telegraph.co.uk/news/health/children/12111882/Children-twice-as-likely-to-be-short-sighted-than-50-years-ago.html In the US, 42 percent of those aged 12 to 54 are now myopic, triple the rate only 30 years ago.5 Wang, Shirley S. “The Puzzling Rise in Nearsighted Children.” 20 April 2015. The Wall Street Journal. 21 January 2016. http://www.wsj.com/articles/the-mysterious-spike-in-nearsighted-children-1429543997 The average rate of afflicted kids worldwide is about 50 percent.

While an increase in myopia among kids might seem trite in view of the fact that diabetes and other potentially deadly conditions are also on the rise, in reality, myopia is a gateway for more serious vision diseases that can lead to blindness. The stretched shape of the myopic eye can cause the inner parts of the eye to stretch and thin, leading to glaucoma, macular degeneration, detached retinas, and even cataracts. One Australian study of 3,600 adults found that 4.4 percent of the subjects with moderate-to-high myopia developed glaucoma, compared to only 1.5 percent of those without. That represents a 300 percent increased risk for those with myopia. A Chinese study found an ever greater correlation, concluding that glaucoma risk was elevated by as much as 7.6 times greater among those with myopia compared to those with normal vision or farsightedness. Data from those same studies also revealed greatly elevated odds of developing cataracts and detached retinas among the myopic subjects.

Why the huge increase in near-sighted kids? In the past, experts blamed heredity, but then a 1969 study in Alaska found a trend that heredity couldn’t explain. Of the 131 original Eskimo subjects in the study, only two had myopia, but a full 50 percent of their children and grandchildren had the condition. Since they all come from the same gene pool, you can’t ascribe the increase to genetics. Next, the experts embraced the idea that excess reading led to near-sightedness. This theory made sense given that kids were spending increased amounts of time in school, particularly in Asian nations where children spend triple the amount of time doing homework compared to kids in the US. Add to that the inordinate amounts of time children spend in front of screens these days. Reading plus screen time would seem to add up to a perfect recipe for myopia.

However, when researchers put the idea that reading leads to myopia to the test in the early 2000’s, it didn’t hold up. In fact, studies showed that there was little correlation between time spent reading and near-sightedness. There was only one factor that consistently correlated to myopia: time spent outdoors. The more time a child spent outside, the less likely he or she would become nearsighted, regardless of heredity or reading habits.

Why would being outdoors help vision? Some experts emphasize that outdoors, the eye becomes accustomed to long viewing distances, and this has a protective effect. Most scientists, however, believe it has to do with light exposure. When the eye is exposed to bright light, the retina releases dopamine. Apparently, dopamine signals the eye to change from night vision, which relies on rod-shaped photoreceptors, to day vision, which depends on cone-shaped photoreceptors. When there isn’t enough light, as in typical indoor conditions, this cycle gets disrupted, with consequences for eye development. It also makes sense that exposure to bright screens at night would further disrupt the natural shift. Research to date supports this hypothesis.

The solution, researchers say, is to increase the amount of bright light children are exposed to. In the US, kids typically spend no more than one or two hours a day outdoors, which isn’t enough. Research suggests that to prevent myopia, kids need to be exposed to at least three hours a day under light levels of at least 10,000 lux. Overcast days may provide less than 10,000 lux even outdoors, but sunny days can provide more than that much even if you’re wearing sunglasses. Indoor settings typically max out at 500 lux.

Clearly, if you live in Finland, it’s going to be difficult to sentence kids to three hours of sunny outdoor time in the winter when it’s cold and dark almost all day long. Researchers are investigating whether using intense indoor lamps that work for seasonal affective disorder (SAD) might help prevent myopia. In China, they’re experimenting with classrooms with glass walls to let in extra light. They’re also working on developing a different type of eyeglass that provides a different range. And there are pharmaceutical eye drops that slow the development of myopia. Of course, there are some side effects ranging from sensitivity to light to dizziness, nausea, tachycardia and hallucinations—but the experts say that the side effects can be reduced at lower dosages with still great results in preventing myopia. In fact, in Asia, the eye drops are quite popular because parents resist letting their kids play outdoors if it means less homework time.

Perhaps drops are easy, but not as easy as simply opening the door and telling the kid to go play outside—or study outside for that matter. Why risk side effects and why pay for drugs when allowing your kids to be outdoors may help them not only avoid nearsightedness, but also may help them stay thin (if they’re actively playing outdoors) so they don’t develop diabetes and all the other conditions that result from sitting on their butts indoors?

Committee on Vision, National Research Council. 1989.Myopia: Prevalence and Progression. 21 January 2016. https://books.google.com/books?id=rIqyPuupuWQC&pg=PT23&lpg=PT23&dq=myopia+rates+1940&source=bl&ots=3kchRGn5-D&sig=_LlTBV0QWAZE_gLUBjm4W2mg7EY&hl=en&sa=X&ved=0ahUKEwiDzu7f4LvKAhVDy2MKHZl-BnQQ6AEIHTAA#v=onepage&q=myopia%20rates%201940&f=false

Harley, Nicola. “Children twice as likely to be nearsighted as 50 years ago.” 21 January 2016. The Telegraph. 21 January 2016. http://www.telegraph.co.uk/news/health/children/12111882/Children-twice-as-likely-to-be-short-sighted-than-50-years-ago.html

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3 Comments

Philip Torrance
on February 10, 2016 at 4:50 pm

. coincident with the. coincident with the increase in myopia,
is a global increase in the use of sugar.
“Duke-Elder in 1925 concluded that hyperopia is less common than myopia
and that ‘the refractive power of the eye
tends to vary directly as the sugar content of the blood;
that is, there is a tendency to hypermetropia with decreased sugar,
with increased sugar to myopia.’
Both Bellows and Roberts agreed with this association
but maintained that diabetic myopia
is less common than diabetic hyperopia.”
“A tendency towards myopia has always been associated with
elevations in blood glucose”
[Br J Ophthalmol. 1982 Aug;66(8):500-5]

Lesley
on February 10, 2016 at 9:29 pm

My siblings and I, born 1952My siblings and I, born 1952,1954,1957, all have myopia, no family history. I needed glasses by 8 years old, before our family had it’s 1st black and white TV. We played outdoors all the time. Reading was not my 1st choice of activities. Live in NZ. Above advice does not seem to fit.

Bruce
on February 20, 2016 at 4:23 am

More time outdoors? CouldMore time outdoors? Could there be a vitamin D connection?

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